Two way switching allows you to control a light from two locations. This is very useful in
a number places, particularly hallways and stairs

To switch from two locations you'll need 2 two way switches and
wire them together in a particular way.

A two way switch has 3 terminals. A common(C), L1 and L2

If you look inside an existing wired in two way switch you will see quite a few wires of differing colours. This can be confusing.

One thing to remember is that the wiriing on light switches is ONLY switching the live wires (NOT the neutral.) If you see black wires or blue wires attched to the switches these are not neutrals. Those wires have just been used for convenience. If done properly they should have a coloured sheath on them to indicate a live wire.

The wiring colours changed a number of years ago from live (red) neutral(black). Now the live is brown and the neutral is blue. (just like you find on the plug of any appliance)

There are several ways to wire two way switching. Below is the way I like to do it. The way I show allows you to fairly easily add a second two way switch to an existing light switch by simply wiring them together in a certain way.